Electrical or electronic switching elements for switching an electrical load which can be activated by electrical signals, that is, which can be switched or actuated, are known from the prior art. In them, the switching state is not changed by a manual activation but rather by an electrical control- or switching signal. They are accordingly to be delimited from manually activated switches.
Electrical switching elements can be constructed, for example, as electromechanical or electromagnetic switches such as relays, contactors, etc.
Electrical switching elements can be constructed, for example as electronic switches or semiconductor switches such as transistors, thyristors or triacs, MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT transistors (Insulated Gate Bipolar Transistor) or IGCT Thyristors (Integrated Gate Commutated Thyristor), etc.
The electrical switching signal for activating electrical or electronic switching elements can be constructed to be either constant or also variable in time, as a function of the usage.
It is known from the prior art to control electrical and electronic switching elements by electrical signals which are based on a pulse-width modulation (PWM), that is, are pulse-width-modulated. Consequently, electrical and electronic switching elements can be controlled by so-called PWM signals.
Furthermore, phase controls for controlling electromotors are known which can represent a type of pulse-width modulation.
A switching arrangement is known from DE 195 22 045 A1 for the power part of a pulse-width modulator for controlling an electrical motor, wherein a transistor is controlled in a pulse-width-modulated manner. Here, an excessive heating of a capacitor which is charged and discharged by the electromotor is prevented, in particular in the case of small pulse widths and low speeds, and the efficiency of the electromotor is significantly improved.
A motor drive circuit for three-phase motors is known from DE 10 2011 050 719 A1 which receives current from transfer devices. These devices consist of a rectifier which produces a direct voltage for a direct voltage intermediate circuit from an alternating current mains voltage, wherein this intermediate circuit feeds an inverter. Inverters operate on the basis of power-electronic switches which are designed, for example, as MOSFET, IGBT transistors or IGCT thyristors. The latter generate a variable voltage by pulse-width modulation, wherein the level of the output voltage and the frequency can be regulated within broad limits in order to drive asynchronous motors as well as synchronous motors.
In order to generate PWM signals, integrated circuits, microcontrollers or also discrete circuits are customarily used which are constructed as a PWM module or can comprise or include such a PWM module. PWM modules for generating the PWM signals are customarily also designated as PWM generators.
In order to be able to control electrical or electronic switching elements by PWM signals, in particular in a reliable manner, it is known to take the technical characteristics of the switching elements as basis when dimensioning these PWM signals. That means that the PWM signals are dimensioned or must be dimensioned in a corresponding manner so that an activation of an electrical or electronic switching element to be controlled in an appropriate manner can be ensured even for the case or cases of very unfavorable parameters of operation or of use.
For example, switching thresholds at which a sufficient voltage and/or a sufficient current for activating an electrical or electronic switching element is/are present, in particular from semiconductor switches such as thyristors or triacs but also from electromagnetic switching elements such as relays or contactors are dependent on the environmental temperature.
Therefore, it is necessary, for example, for a reliable ignition of a thyristor or of a triac, especially in order to ensure a reliable ignition of a thyristor even in the case of a sharply rising main current, that an electrical control impulse is present with a sufficient current amplitude, for example, with a fivefold gate current and a current slope greater than one ampere per microsecond. The necessary ignition impulse is dependent here on the chip temperature of the thyristor.
As a consequence, the required ignition current for, e.g., thyristors and triacs is heavily dependent of the temperature of the semiconductor. At low temperatures a higher ignition current is needed. However, a higher ignition current leads at high temperatures to unnecessary losses.
In addition, even the voltage supply of the electrical or electronic switching elements can be basically variable or not always constant, for example when using non-regulated mains parts for the voltage supply.
Therefore, preferably integrated circuits or microcontrollers are used for generating the electrical signals for controlling the electrical or electronic switching elements. However, since microcontrollers in general cannot make the necessary energy available for activating the switching elements, in particular not the necessary ignition energy for the control impulses of thyristors, additional end amplifier stages must often be used for strengthening the electrical signals.
End amplifier stages can basically be supplied with variable supply voltages. To this end economical, unregulated mains parts can be used which, however, have a variable output voltage, for example, for supplying devices with 24 volts and in an operating range of 18 to 30 volts.
In order to take into account the above-described problems of fluctuating environmental temperatures and or supply voltages, it is therefore customary to dimension PWM signals for electrical and electronic switching elements in a corresponding manner so that an activation of an electrical or electronic switching element to be controlled in a corresponding manner can also be ensured for the case or cases of very unfavorable operating parameters, for example, in the case of the lowest acceptable supply voltage and/or environmental temperature.
However, this procedure in the dimensioning of PWM signals has the disadvantage that given the presence of other operating parameters, for example, given a very high ambient temperature and/or supply voltage, very high losses are the consequence, in particular associated with low efficiencies and/or damage to the electrical or electronic switching elements or with other consequential damage.
Therefore, the smallest admissible supply voltage and the lowest ambient temperature, for example, 18 volts and −25° C. are preferably used and taken for the dimensioning of electrical and electronic switching elements and correspondingly high losses in operating parameters of, for example, 30 volts and +70° C. Celsius are accepted.
Given this background, the invention has the particular problem of making a possibility available for controlling electrical or electronic switching elements which can be activated by an electrical signal in a simple, reliable and/or secure manner and to also further reduce, if possible, electrical losses more and to raise the energy efficiency and the economy of these switching elements.
The above-cited problems are solved by the features of the independent claims. Preferred further developments are subject matter of the dependent claims.